CUSTOM CONTACT LENSES
Due to the variations in Keratoconus, no one fitting regime is perfect for all cases.
Custom have been involved with Keratoconus for
many years and we find that the following 3 types of fitting will work well if correctly applied for this type of patient.
RGP Keratoconus lenses with diameters from 8.80 mm to 10.20 mm and base curves from 5.50 mm and up will fit for most early to
middle stage keratoconus with reasonably centred cones. The problems arise for decentred cones, especially from PMD in which the cone
is low and nasal or low and temporal, these require assistance to help with lens centration (Piggy back with groove) or better
still to vault the cornea using the Stoker semi scleral lenses (13.50 or 14.50mm diameter) These are proven designs used for
more than 20 years with an extremely high success rate.
All the above types of lenses must be fitted from a diagnostic set, which
is available from Custom on loan or can be purchased.
Note no 2 keratoconus patients are the same so you must be flexible in your fitting
to maximise comfort and vision for your patients.
Do topography and note the centre of the cone. Note K readings and corneal height. Utilising the Topographers features look at the
3 D image. Next look at the fourier images for irregular astigmatism.
From the above you can feel confident in knowig the stage
of the 'cone. If early to mid then utilising the standard Custom diagnostic set, fit a lens which you feel should be good.
Check the fluoresceine image with the lens centred on the cornea, and assess if too steep or flat. If the picture shows excessive touch
(note you will see the apex of the cone quite clearly) then go 2 or 3 steps steeper and repeat. When you just get clearance
then go back (ie flatter) by one step. This should be the optimal base curve. Note the position of the lens and the amount of
edge stand off. Over refract this lens and order, adjusting the edge lift as required. (increase for more edge lift and decrease for
For better centration you can go larger in diameter or if dealing with tight lids smaller. Adjust the base curve
Note it may take more than one lens to obtain the optimum fit.
I find that if a patient is shown the topography, they get
a better understanding of their problem and the complexities involved in the fitting.
If the 'cone is well off centre then consider
going to a Soft lens Piggy back, (Our lens has a groove to hold the lens centred) or consider a Stoker Semi scleral design (my preference)
Always use the highest DK material compatible with stability and wetting. We strongly suggest the Silperm 100 for all RGP Keratoconus fits and the 125 Dk material for early 'cones.
There is no contest here as Topography is essential when fitting keratoconus patients. As keratometry only measures the central 3 or 4 mm you do not get a true picture of the cornea and it is impossible from keratometery to know what lens is required.
Often you will pick up an early Keratoconus from doing routine Topography, note that long time soft lens wearers may show signs which have been masked by the soft lenses.
Keratometetry Vs. Topography